edge-layout in graphviz for fixed node positions

Question

I was trying to write my own little algorithm for graph layout that only creates a node layout but does not define edge routes. When I use Graphviz to turn the resulting dot file into a graph, the edges are straight lines that cross the nodes and even overlap each other. Is there a way to use Graphviz to layout the edges as nicely as the dot algorithm does, but have the nodes in predetermined fixed positions?

You can see the effect for instance on the following graph:

digraph test {
  "a" [pos="0.0,0.0"];
  "b" [pos="50.0,50.0"];
  "c" [pos="100.0,100.0"];
  "a" -> "b";
  "a" -> "c";
  "b" -> "c";
}

When drawn with dot -Knop -Tpng -otest.png test.dotty the line between a and c crosses b. What I want is that all nodes keep their positions, but the line between a and c goes around b.

Answer 1

Just add:

splines=true;

to your graph - result is: